Telephone system



H. M. BAscoM EAL TELEPHONE sYs-TEM July 9, 1946.

Filed Jan. 15,: l1945 5 sheets-sheet 1 HM. @Asco/w N V 5^ T @RSF/1. HUBBARD ATTORNEY July 9, 1946.

H. M. BASCOM ETAL TELEPHONE SYSTEM Filed Jan.y 13, 1945 ,HMB/1560,14 Nm/TOMBA. HUBBARD B Q? 6. M

ATTORNEY July 9, 1946. HgM. BASCOM E-rAL 2,403,475

TELEPHONE SYSTEM Filed Jan. 13, 1943 5 Sheets-Sheet 3 FA. HUBBARD By ,4 fro/QMS y -l/WE/vrons H M BASCOM July 9, H M BASCOM ETAL TELEPHONE SYSTEM Filed Jan. l5, 1945 5 Sheetg-Sheet 4 H. M. @ASCOM NVE/V70 EA. HUBBARD B y 6.26. M

A TQQ/VE y -July 9, 1946. u H. M ZBAsc-OM l-:T Al. l K 2,403,475

TELEPHONE SYSTEM Filed Jan. 15, 1945 5 sheets-sheet 5 FIG /4 y HMB/ISCOM. /NVE/V'RS l f f v v ATTORNEY Patented July9, 1946 UNITED STATES AParleur-T lori-ica TELEPHONE SYSTEM Henry M. Bascom, New York, N. Y., and Francis A.

Hubbard, Maplewood, N. J., assignors to Bell. Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 13, 1943, Serial No. 472,202

y 7 Claims. lV

This invention relates to telephone systems and more particularly to a system employing a call transmitter which is an improvement over the telephone call transmitter disclosed in United States Patent No. 2,315,344, granted March 30, 1943, to R. F. Mailina.

In the transmitter described in that application a set of key members is used for actuating U-shaped bars in predetermined combinations for releasing normally pretensioned vibrative elements or reeds in similar-combinations, by the operation of latch members or pawls normally holding the vibrative elements in their pretensinned positions. the operation ofthe vibrative elements in the magnetic eld of the generator being eiective to transmit signals corresponding to the numerical values of the successively operated members.

In this transmitter ve vibrative elements having five different fundamental frequencies are employed which elements are released for/vibration through the operation of five U-bars which are allocated respectively to the five vibrative elements. 'Ihe U-bars are operated in different combinations of two at a time by the depression of the different keys of the ten-button key-set thereby resulting in the release of the vibrative elements in corresponding combinations of two at a time. The release of the vibrative elements occurs for a brief interval only during the depression movement of l a key-set key. The characteristics of the vibrative elements may be so chosen that their vibration in the magnetic eld of the generator causes the generation of currents of, for example. 700, 900, 1100, 1300 and 1500 cycles.

Studies of this transmitter and the operation thereof havey indicated to the applicants that there would .be several advantages if the vibrative elements could be released for vibration either during the down-stroke or the up-stroke of an operated key-set key. The studies which have been made of the time intervals required for the satisfactory registration of the. signals transmitted by a substation generator of the type just referred to and observations of the speed with which the keys of the key-set areoperated indicates that it would be possible to generate a signal impulse which could be registered `accuratelyon either or both the down-stroke and the up-stroke of a key-set key. VIn receiving circuits which have been developed for use with the ca ll transmitter above referred to a signal duration of` 20 to 25 milliseconds or less is all that is utilized for effecting a registration of such. signal.

the major portion of the signal being consumed in the functioning of the unit of the receiving circuit which indicates that a signal is present and which activates thereceiving channels of the receiving'circuit for a period of 5 to 8 milli seconds. Since it appears to be unusual for a key stroke to be completed in less than milliseconds, it would therefore be entirely possible to secure two separate signals on each key stroke.

The principal advantage which is gained from this method of operation islthat the number of vibrative elements may be reduced from ve to three. since the selective release of the three members may be made rst during the downstroke of any key to send one signal impulse and again during the up-stroke of the key to send a second signal impulse.

sponding reduction of the number of receiving channels required in the receiving circuit at the 'central ofiice. This reduction permits the frequency spacing between channels to be doubled for the same outside frequency. range which would reduce the discrimination required from channel filters. For example, the channels could be designed to be responsive to signals of the three frequencies 700. 1100 and 1500 and, of course, the vibrative elements of the call transmitter would be selected to cause the generation of such frequencies. Alternatively. the outside frequency range could be made smaller so that the difference in attenuation `between the highest and lowest frequencies would be less.

It is, therefore, the object of the present inv vention to arrange a call transmitter of theree leased reed type so that the reeds thereof are selectively released on the down-stroke and on' These objects are attained by the provision of mechanism in a call transmitter of the type dis' closed in the patent to Mailina hereinbefore referred to, whereby the operation ot anyone of The reduction of the number of vibrative elements enables a correthe ten keys o f the key-set is eective upon the down-stroke to selectively release one of three I vibrative elements or reeds and is effective upon its up-stroke to selectively release one or more of the three vibrative elements. In the proposed transmitter only three vibratve elements or reeds are required. To pluck these reeds a releasing mechanism of the improved type disclosed for example in United States Patent No. 2,307,537, granted January 5, 1943, to D. B. Parkinson, may be employed. The reed-releasing member associated with each reed is operable by a cam four times during each revolution of the cam. vEach cam has two ratchet wheels connected thereto, each of which ratchet wheels may be advanced through four steps per revolution by an associated stepping pawl which is pivoted to the end of a pawl lever connected to a U-bar. The two pawls associated with the two ratchet wheeis connected to each cam are disposed so that the cam is advanced one step or quarter `revolution upon the operation of the U-bar to which one of the two pawls is connected and may be advanced a second step or quarter revolution upon the release of the U-bar to which the other of the two pawls is connected.

Of the six U-bars thus required three are instrumental when operated in response to the down-stroke of certain keys of the key-set to cause the selective releasing ofthe three reeds and the other three are instrumental when released in response 'to the up-stroke of certain keys of the key-set to cause the selective releasing of the same three reeds. The selective releasing of the reeds in response .to the downstrokes and 11p-strokes ofthe ten key-set keys causes the generation of signals of the three frequencies a, b andV c which might, for example, be of '700, 1100 and 1500 cycles frequency.

A code may be so selected with respect to the standard arrangement of the keys in the key-set as indicated in a` table appearing hereinafter that every key releases a single reed on the downstroke and that no two adjacent keys arranged either vertically or horizontally release the same -reed on the down-stroke. Hence, if two keys are depressed at once, two reeds will be released and the receiving circuit can be arranged to recognize this as a false signal.

The transmission of two signal impulses by the call transmitter for each keyed digit requires a modification of the receiving circuit associated with the central oilice sender, whereby three receiving channels are provided to receive the three diierent frequencies transmitted by the call transmitter, with each of which channels two groups of. recording relays are associated. Each of these groups of relays comprises a relay correspending to each of the three frequencies, one group being normally associated with the three receiving channels so that one of such relays is selectively operable in response to the'reception of one of the three frequencies Vtransmitted upon the down-stroke of an operated key andthe other group being associated with the three receiving channels following the termination of the nrst impulse of a digit signal so that relays of such group are selectively operable in response tothe reception of one or more of the three frequencies transmitted upon the up-stroke of the operated key. Thus upon the termination of the two impulses of a digit signal a relay of the first group and one or two relays of the second group will remain operated to control the setting of a digit register of the sender.

sembly shown in Fig.

For a clearer understanding of theinvention reference may be had to the following detailed description taken in connection with the accompanying drawings in which:

Fig. 1 is a side elevation view of the telephone call transmitter embodying the invention, the casing being shown with a portion broken away to disclose the reeds in their pretensioned positions and to disclose the key-operated reed-releasing mechanism;

Fig. 2 is a side elevation view similar to Fig. 1 but in which a portion .of the reed-releasing mechanism is shown in the position assumed upon the depression of a key and one of the reeds is shown released for vibration;

Fig. 3 is a top view of the call transmitter with a portion of the casing broken away; J

Fig. i is an enlarged detail view showing a reed-releasing mechanism in the normal position in which the associated reed is held pretensioned;

Fig. 5 is a detail view similar to Fig. 4 showing the reed-releasing mechanism in its operated position in which the associated reed is freed for vibration;

Fig. 6 is a top plan view of sociated ratchet assemblies reed-releasing members;

Fig. '7 is a front elevation View of the cams and associated ratchet assemblies;

the cams and asfor operating the Fig. 8 is a side view, with a portion cut away,r

of one of a pair of cam operating ratchet assemblies shown in vits normal position and effectivel when moved to the position shoyvn in Fig. 9 upon the down-strokeof a key-set key to rotate the associated cam when the operated key returns to 'normal on its up-stroke;

of the other of a pair of cam operating ratchet assemblies shown in its normal position and effective during its movement to the position shown in Fig. 11 in response to the down-stroke of a keyset key to rotate the associated cam;

Fig. 11 is a side view of the ratchet wheel as- 10 in the 'position to which it. is moved at the fmd of the down-stroke of a key-set key; and

Figs. 12, 13 and 14 taken together show a telephone system to which the improved call transmitter is applicable; Fig. 12 showing the substation circuit in which the call transmitter is installed, a diagrammatic illustration of a line iinder first selector, a sender link comprising a trunk finder and a sender selector, and a portion of the circuits of a central office sender; Fig. 13 showing the receiving channels of the sender, the recording relays and other control relays; and Fig. 14 showing certain of the sender registers and progress relays associated therewith.

In the call transmitter of the invention as shown in Figs. 1, 2 and 3, a base I is provided having up-turned edges 2 to which the molded casing 3 is attached. Secured to the base I is a mounting plate l having up-turned ears 5 and 6 for supporting a shaft 1 on which the key members Kl to K10, inclusive, are pivotally mounted; an up-turned and then in-turned bracket 8 upon which the off-normal switch assembly 9 is se cured by the screws l0; an up-turned ear Il the purpose of which will be later discussed, and an up-turned plate l2. Each of the key members KI to KID, inclusive, is normally and yieldably maintained in the position disclosed in Fis. 1 bya retractile spring I3 each of .which springs is hooked at one ofits ends to a key member and at the other of its ends to the upper edge of the plate I2.

Also pivotally mounted ou the shaft 1 are six U-bars BI to B6., inclusive, which are operable in different combinations upon the depression of the key members. These bars are normally and yieldably held in the position disclosed in Fig. 1

by retractile springs I4 which are hooked at one of their ends to the upper edge of the plate l2 and at their other ends are hooked to the lugs I5 of lever members I6, I'I, I8, I9, 20 and 2| which are secured to the U-bars BI, B2, B3, B4, B5 and B8, respectively, as by rivets 22.

A U-shaped oli-normal bar Bl is also pivoted on the shaft I and is held in operable relation with each of the ten key members KI to Kill, inclusive, by'aretractile spring 23, hooked at one of its ends to a lug on the lever 2li, secured to the bariBl as by rivets and at the other of its ends to the plate l2. The lever 24 is effective to control the od-normal switch assembly el once when any key ofthe key-set is operated on a down-stroke through the operation of the offnormal bar Bl and again when the operated key is released in an up-stroke. v

'I'he off-normal switch assembly may be of the type fully disclosed in the copending application Serial No. 470,724, led December 31, 1942, in the name of F. A. Hubbard. In general it comprises a permanent magnet to the pole faces of which are attached two parallelly extending polepieces having aligned holes therethrough in which is supported a switch element 25 of the mercuryr contact type. A. switch element of this type is disclosed in Patent No. 2,295,602, granted September 15, 1942, to C. E. Pollard, Jr., and has the characteristic that when its armature is op- 6 other to provide pole faces between which free ends of the reeds may vibrate. Positioned on the upper surface of the pole-piece PI is a bracket member 28 having two downwardly extending ears 29 between which the latchingmember'30 is pivotally'supported on the pin 3l, 'I'he previously described .elements of the generator able manner as by screws (not shown) extending through holes in the plate and separator 34 into threaded holes in the pole-piece P2. .I

Positioned between the pole-pieces Pl and P2 in the space between the ends of the magnets MI and M2 and the inner faces of the in-turned ends of the pole-pieces is a coil 35 having a central vsleeve through which the reeds Re, Rb and Rc extend with sufllcient clearance to permit them to vibrate freely.

The latching member 3b, as best disclosed in Figs. 4 and 5, is substantially l.shaped having ears Stat its ends which serve as bearing members by which the member is pivoted on the pin 3l.

ber 30 is normally positioned as disclosed in Fig.

l with its upper. edg'e positioned beneath the ends of the three reeds Ra, Rb and Rc. The hori erated a contact member movingv therewil-,hV

quickly disengages a. back contact member and quickly engages a front contact. member, but that when the armature is lreleased the movable contact member is slow to break away from the front contact member. Normally the switch element is prevented from operating in the eld of the iiux set up by the permanent magnet, by a low re` luctance shunt member 28 held in bridging en sagement with the pole-pieces of the off-normal switch assembly by a retractile spring 2l. The

` end of lever 24 is so positioned with respect lo a cam surface on the shunt member 26 that when the end of lever 24 is lowered in response to the down-stroke of any operated key, the shunt 'is momentarily cammed away from the pole-pieces to permit one operating cycle of the switch element and that when the end of lever 24 is raised in response to`the up-stroke of the operated key, the shunt is vagain momentarily cammed awayA from the pole-pieces to permit a second operating cycle of the switch element. The off-normal 4switch assembly is effective to transfer the subelem nts or reeds Ra, Rb and Rc the characteristics of which are so chosen as to give these elements different natural periods of oscillation. Associated with the outer pole faces of the 'magend of its finger 48 engaged against the reed with zontal arm 38 of the latching member is ncrmally engaged by the ends of leaf springs at can. ried by the reed releasing members dit.

For releasing each of the reeds forv vibration a releasing member t, operating cam il and a pair of cam-operating ratchet assemblies l2 and t3, are provided. The operating cams and assovciatecl ratchet assemblies are mounted for rotation on a pivot screw t2 which is supported in the ear llv and in the bracket d4 which bracket may be secured to the base plate l in any suitable manner as by rivets d5. The releasing roembers di! are each provided with a slotted vertical arm tt, a horizontal latch-operating projection ll and a vertically extending reed-releasing finger 48. The members it are supported for vertical movement on rods 4a which-extend through holes in the ear ll and bracket 44 and' through the slots in the members et. For spacing the members 40 for alignment with the reeds with which they function respectively, tubular spacers 50 arepositioned on the rods 49; Each releasing member 40 is normally held with the which it cooperates v--to pretension suchreed as disclosed in Fig. 4, by a leaf spring 5l which is secured at one end to the base plate 4 as 'by a rivet 52 with its free end engaged beneath the member 40. The upper end of the vertical arm net are two L-shaped pole-pieces PI and P2, the f short arms of'which are in-turned towardl each 46 of each member 40 is provider.. with a rounded cam surface 53 which is normally engaged in the depression between two lobes of the associated Voperating cam 4I.V Each operating cam 4l is provided with four camming lobes and is' secured to a 'sleeve 54. Also secured .to the sleeve 54 on one side of the cam 4l is the ratchet wheel 55 of a ratchet asvsembly 42 and on the other side of the cam is l.the ratchet wheel 56 of a ratchet assembly,

each of which ratchet wheels is providedwith four teeth equally spaced around its periphery. lAs disclosed in Figs. 8 and '9 each ratchetas- 'the' The vertically disposed arm 3l of the mem- 1 .turn connected to one of the U-bars, such as B5. The pin i also extends through aligned holes in the parallelly disposed walls of a housing 62 which embraces the faces of the ratchet wheel 55. The housing is also provided with other aligned holes through which extends the sleeve 54 on which the ratchet wheel 55 is secured. The

` thekeys -of the key-set the housing 55 is rotated walls of the housing are united by web 53 to which one end of a leaf spring 6d is secured, the free end of such spring being engaged with one arm of the pawl 51 whereby the other end of such pawl is held yieldingly in engagement with the periphery of the ratchet wheel 55.

By virtue of the journaling of the housing 52 on' the sleeve 54 and the pivoted connectionA of the pawl arm 58 to such housing, the housing and pawl 5l are rotated about the sleeve 55 as an axis upon either the downward or the upward movement of the pawl arm 58. The normal position of the pawl 51 with respect to the teeth of the ratchet wheel 55 is disclosed in Fig. 8. When, however, a U-bar and lever member connected thereto are depressed by the depression of one of the keys of the key-set the housing 62 is rotated by the pawl arm 58 in a counter-clockwise direction whereby the pawl 51 moves freely over a tooth of the ratchet Wheel 55 Without causing the rotation of such ratchet wheel until, when the U-bar has become fully depressed,`

the ratchet assembly assumes the position disclosed in Fig. 9. In this position the end of pawl 51 has been forced by the spring 64 to engage beneath a tooth of the ratchet wheel 55.

When thereafter the operated key is released resulting in the restoration of the depressed U- bar, the pawl arm 58 moving upwardly causes a clockwise rotation of the housing 62 and pawl 51, thereby causing a rotation of the ratchet wheel 55 and associated cam 4| through a quarter of a revolution.

As disclosed in Figs; 10 and 11 each ratchet I wheel assembly 43 comprises a. ratchet wheel. with which a pawl 59 is adapted to cooperate. The pawl 59 is pivoted bythe pin 55 to the lower end of a pawl arm the upper end of which is pivoted to the forwardly extending arm of a lever member, such as 20, which is, in turn,

connected to one of the U-bars, such as B5. The pin 65 also extends through aligned holes in the parallelly disposed'walis of a housing 55 which embraces the faces of the ratchet wheel 55. The housing is also provided with other aligned holes through which extends the sleeve 54 on which the ratchet wheel 56 is secured. The walls of the housingv are united by a web 51 to which one end of a leaf spring 58 is secured, the other end of such spring being engaged with the pawl 59 whereby the pawl is held yieldingly in engagement with the periphery of the ratchet wheel 55.

By virtue of the'journaling of the housing 55 on the sleeve 54 and the pivoted connection of the pawl arm 60 to such housing, the housing and pawl 53 are rotated about the sleeve 54 as an axis upon either the downward or the upward movement of the `pawl arm 60. The normal position of the pawl 53 with respect to a. tooth of the ratchet wheel is disclosed in Fig. 10. When, howeven' a U-bar and lever member connected thereto 'are depressed by the depression of one of by the pawl arm 50 in a clockwise direction whereby the paw1 59 normally engaged with a tooth of the ratchet wheel 55 rotates suchratchet wheel and connected cam 4I through a quarter revolution until the ratchet assembly 43 assumes the position disclosed in Fig. 1l at which time the U-bar has become fully depressed. When thereafter the operated key is released resulting in the restoration of the depressed U-bar the pawl arm 50 moving upwardly causes a counter-clockwise rotation of the housing 66 and pawl 59 whereby the pawl 59 moves freely over a tooth of the ratchet wheel 55 without causing the rotation thereof.

From the foregoing description of the ratchet whee1 assemblies d2 and 43 it will be noted that the assembly c3 causes a quarter revolution of the associated cam ci on the down-stroke of a key-set key and the consequent down-stroke of a U-bar, such as B5, and that the assembly 42 causes a quarter revolution of the associated cam 4i on the up-stroke of an operated key and the consequent up-stroke of the previously operated U- bar. Thus, U-bars Bl, B3 and B5 through which the three ratchet assemblies 43 are operated, may be considered to be down-stroke bars and the U-bars B2, B4 and B6 to which the three ratchet assemblies 42 are operated may be considered to be up-stroke bars. l Any cam 4l' may thus be rotated under the control of either an associated down-stroke U-bar, such as B5, or an associated up-stroke U-bar, such as B5.

To illustrate the manner in which the call transmitter functions, it will be assumed that the key member Kl for transmitting impulses of a code for the digit lis depressed. By reference to the following table, it will be noted that for the digit 1 it is necessary to transmit an impulse of the frequency a during the down-stroke of the key KI 'and to transmit a second impulse of the frequency a during thev up-stroke of key member Kl To accomplish this the under-surface of the key member Kl is provided with an extension i3 .which engages with the upper edges of both the U-bars B6 and B5 so that upon the down-stroke of the key member both of these U-bars are depressed. The depression of the U-bar B5 through the associated lever member 25 and pawl arm 6u causesv a quarter revolution of the camv 4I which momentarily depresses the releasing member 40 associated therewith and with'the generator reed Ra.' Upon the downward movement of the member 40 the spring 39 is moved away from the horizontal arm 38 ot the latching member 30, the end of nger 43 is moved away from the reed Ra to permit the reed to engage with the upper edge of the vertical arm 31 of the member 30 and thereafter the projection 41 of member 40 engages the horizontal arm 38 of member to rotate such member about the pivot pin 3| to remove its vertical arm 31 from beneath the end of the reed. The Reed Ra is thereby freed from its pretensioned position and vibrates within the coil 35 and between the pole-pieces PI and P2 of the generator G, Current of the frequency a is thereby generated in the coil 35 and transmitted therefrom over the substation line.

When the releasing member 40 restores to its normal position under the influence of the spring 5i after the operating cam 4l has completed a sition and the spring 3s carried by the member 4l engaging with the arm 38 of the latching member 30 moves the vertical arm of such member beneath the end of the reed as disclosed in Fig. 4.

The depression of the U-bar B6 through the associated lever member 2| and pawl arm 58 lis ineective to rotate the cam 4| during such down-stroke movement of the bar but the pawl 51 of the ratchet assembly 42 is so positioned that upon the up-stroke movement ofthe bar B8 when the key Kl is released, it is eii'ective to rotate the cam 4| through a second quarter revolution and to thereby again cause the release of the reed Ra in the manner previously described to generate a second impulse of `current of the frequency a and to transmit it over the substation line.

The keys Kl to K|0, inclusive, of the key-set are so designed that they are effective to operate the U-bars BI to B6, inclusive, to control the generation o f current of the frequencies a, b and c in the manner indicated in the following table:

The call transmitter of Figs. 1 to 11, inclusive, is applicable to a, wide variety of types of dial switching systems and, particularly to those of the type in which register mechanisms are employed at the central oiiice for registering the des- 10 larger areas cnice codes require two or three ofiice code digit registrations and the numerical part of the designation usually requires four registrations. In the present disclosure three cnice code digit registers A,.B and C are shown inFig. 14 and the units numerical register U is also shown, it being understood that the thousands, hundreds and tens'registers would be provided vand inserted between the units register U .and the code digit register C. These registers each comprise five register relays which are selectively operated under the-control of the six recording relays AD, BD, CD, AU, BU, and CU, and the frequency re-y ceiving channels Fa, Fb and Fc of Fig, 13.

vIt will be assumed that the subscriber at the substation illustrated in Fig. 12 -I removes the handset H of the subset from the cradle to initiate a call whereupon a circuit is established over the substationl line to thev central office' which is ln- Y of the sender with the substation a circuit is es-` ignation transmitted and for controlling theselective operation of automatic switches to complete connections. Accordingly, Y the system chosen to illustrate the invention is one in which the central oflice is equipped with automatic switches of the panel type and with register senders for registering the designations transmitted to the central ofiice from subscribers stations. It will be obvious that other formsof switches may be used for establishing the connections such as switches of the cross bar type and switches of the well-known step-by-step type.

Referring to Figs. 12, 13 and 14 of the drawings, a subscribers line is shown appearing in the contact bank of the line finder LF. The line finder is joined to a first or district selector S and these two switches together form a link for extending subscribers lines to trunks extending to other selectors (not shown) by which a connection from a calling subscribers line may be extended to a wanted subscribers line. The line finder and district link have access through a sender link SL comprising a trunk finder TF and a sender selector SS to a plurality of' common register senders. Figs. 13 and 14 disclose such parts of a sender as are necessary for an understanding of tablished from battery over brushes of the trunk A finder TF and sender selector SS, conductor |200,

and windings of relay |300 to ground. Relay |300 operates and closes an obvious operating circuit y for relay |302. Relay |302 upon operating connects ground over its right contacts to the 011-. normal conductor |303 to provide locking ground for other relays of the sender and over its left conitacts and conductor |304 establishes the circuit of relay |20|. t

With ground connected to conductor |303 a circuit is established therefrom over the left back contact of relay |309, conductor |3|0 to battery through the winding of lprogress relay i406 whereupon relay |408 operates and locks in a circuit from battery` through its winding and the winding of progress .relay |401, over the inner left front contacts of relay |403 and over the back contact of 'progress relay i4|1 to ground` on con- `ductor |303. Relay |401 does not operate in this locking circuit'since its winding is shunted so long as ground remains connected to conductor |3|0. lWhen relay |406 operates a circuit is also established from ground on conductor |303, over the back contact of. relay I4 1, the outer left contacts of relay |406, conductor |3I and to battery through the right normal contacts and winding of relay |309. Relay |309 thereupon operates, locks over its rightalternatecontacts to ground on conductor |303 and at its back contact removes ground from conductor |3|0 whereupon relay |401 operates in the locking circuit of relay |406;

prepares operating circuits for the relays of the first code digit register A over Aconductors |33l, |332, |334, |335 and |330 and at its right contact connects ground to conductor |30| to shunt the right winding of relay |300 whereby the current flowing over the operating circuit of relay |300 is increased as a signal to the line-finder selector link.

Relay I20| upon operating connects the windings of battery feed relay |202 tothe calling line substation over a circuit which may be traced from batterythrough the left winding of relay |202, the left contacts of relay |20I, brush |203 of sender selector SS, brush |204 of the trunk finder TF, contacts of sequence switch cam |205, brush |208 of line finder LF, the ring conductor of the calling line, switchhook contacts |201, the back i l l contact of the off-normal switch assembly 9, through the transmitter |206, the left winding of repeating'coil |209, the tip conductor of the calling line, brush I2 I0 of the line-finder LF, sequence switch contacts |2| I, brush I2|2 of trunk finder TF, brush |2|3 of sender selector SS, right contacts of relay |20|, right winding of relay |202, normal contacts of relay I2|0 to ground through the secondary winding of the dial tone coil I2I5. Relay v|202 operates over this circuit and dialing tone current is applied thereover to apprise the calling subscriber that he may proceed to key up the digits of the desired telephone number. Relay |202, upon operating, establishes an obvious circuit for relay I2|0 which also operates to prepare an operating circuit for relay |2I4, and relay |202 establishes a circuit from ground over its left contacts, conductor 12H, cverthe upper normal contacts and through the winding of relay |305,'and through resistance i301 to battery and in parallel therewith through the winding of relay I 306 and resistance |308 to battery. Relay |306 operates and locks over its upper alternate contacts to ground on conductor |303 but the winding of relay |306 being shunted so long as ground is applied to conductor |2I1, does not operate. The closure of the lower front contact of relay |305 is without function at this time.

In response to the reception of dial tone the calling subscriber proceeds to key up the digits of the wanted line number, which number it will be assumed is CH3-1067. When the key K2 which, in addition to the digit value 2 has the letter designations ABC, is depressed to transmit signal impulses for the first code letter C, the off-normal switch assembly 9 is momentarily operated and then released during the down-stroke of the key and in the interval that the movable contact of such switch assembly is in engagement with the front contact thereof a reed of the generator G is caused to vibrate to generate a current impulse cfa predetermined frequency. Again when the depressed key is released the off-normal switch assembly' 0 is momentarily operated and released and during the interval that the movable contact thereof is in engagement with its front contact, a reed will be vibrated to generate a second current impulse of a predetermined frequency. By referring to the preceding table, it will be noted that when key K2 is depressed, the frequency c is generated both upon the down and upstrokes thereof. 'I'his frequency might', for example, be of 1100 cycles. 4

The movement of the movable contact of the off-normal swltch'assembly S from its back or normal contact position disconnects the subset transmitter |200 from its bridged connection across the substation line and the engagement of the movable contact with the front contact connects the coil 35 of the call transmitter generator G across the line through the condenser |2|8. There being no direct current bridge across the substation line at the substation so long as the movable contact of the off-normal switch assembly 9 is out of engagement with its back contact, relay |202 of the sender releases in turn opening the circuit of relay |2| 6 and removing ground from conductor |2|1. Relay |2|6, however, being slow to release does not release during the interval that the movable contact of the off-normal switch assembly 9 is disengaged from its back contact. With relay |202 released and relay |2|6 operated an obvious circuit is establishedfor relay |2I4 which operates and at its contacts discoil |2|5 from 'the calling line loop 'to discontinue the application of dial tone current thereoverand connectsrdirect ground to the calling line loop. I'he removal of ground from conductor |2 I1 removes the shunt from the winding of relay |300 which now operates in a circuit from ground on conductor |303, over the upper alternate contacts of relay |305, through the winding of relay |306 and resistance |308 to battery.

When the first impulse of current of the frevquency c is transmitted over the line, it passes over the 'previously traced circuit through the sender link, through the broadband-pass filter I2| and the primary winding of the transformer |220 and is impressed through the circuit X and the primary windings of the input transformers associated with the receiving channels Fa, Fb, Fc and V. Associated with each input transformer, such as ISIS, is a frequency receiving channel consisting of a secondary winding of such transformer, a series tuned circuit I3 I4, a single vacuum tube such as I3I5 with a feedback through the copper-oxide units, such as I3|6, and a relay, such as |3|l. Initially, the vacuum tube is biased nearly to cut-off. A small received signal is amplied andfed back. through the condenser I3I8 and the copper-oxide units |3|6 to charge up the condenser I3|9. This condenser is poled to reduce the negative bias on the grid of the tube |3|5 with the result that the gain of the tube is increased and the amount of voltage on the grid is increased further. The rlnal result is that a relatlvely small signal is suiiicient to produce a sharp rise in plate current through the relay |3|l. The

sensitivity of each individual channel is adjusted by means of the variable resistance, such as |320. This method controls the sensitivity by changing the alternating current feedback and does not affect the tuning of the channel.

From the preceding description it will beapparent that each relay, such as relay |3Il in each channel, will respond to a single frequency with a relatively high discrimination against the others. In the present description it has been assumed that the `first channel Fa is tuned to the a frequency of 700 cycles; the second channel Fb is tuned to the b frequency of 1100 cycles; and the third channel Fc is tuned to the c frequency of 1500 cycles.

Upon the receipt of the first impulse of frequency c the channel Fc responds resulting in the operation of channel relay 63H. Relay |3|l upon operating establishes a circuit from ground over its contacts, the middle right back contact oi' transfer relay I 32|, through the winding of recording relay CD to battery. Relay CD thereupon operates, locks over its inner left contacts to ground over the back contact of release relay |322 and at its outer left contacts prepares a circuitfor relay |32I. Upon the termination of the signal impulse when the off-normal switch assembly 9 reestablishes the direct current bridge at thesubstation through the subset transmitter, relay |202 reoperates to establish the circuit of relay |2|6 and to reconnect ground to conductor I2I1 whereupon such ground islextended over the upper front contact of relay |306 to a point between the winding of'relay |305 and resistance |301. Relay |305 being now shunted releases.. Relay |306 is, however, maintained operated following the release of relay |305 over a circuit from ground on conductor I2I'l, over the upper normal contacts of relay |305, through the winding' 0f relay |306, and resistance |308 to batconnects the secondary winding of the dial tone u tery. With relay |305 released and relay |366 13 heldl operated the circuit or relay |32| is now completed from ground over the lower back con- .tact of relay |305, the inner lower front contact of relay |305, the outer left contacts of relay CD tol battery through the winding of relay |32|.

Relay |32| now operates; locks over its inner right front contact to ground over the back contact of relay |322; at its back contacts disconnects the Iwindings of recording relays AD, BD and-CD from the contacts of the channel relays |323, |324 and |3||, respectively; connects the windings of recording relays AU,` BU and CU with the contacts yof the channel relays, all of which are at this ground over'the contacts of relay 3| 1, the mid-- dle right front contact of relay |32| to battery throughjthe winding of recording relay CU. Relay CU fupon operating locks over its left front contact to ground over the back contact of relay When the off-normal spring assembly again releases to terminate the second frequency impulse the reoperation of relay |305 over the circuit previously traced is effected by the reoperation of relay |202. With relay |305 operated and relay |305 unoperated a circuit is established from ground over the lower front contact of relay |305, the lower back contact of relay |300, the

- right-backl contact of relay AD,` the No. 2 right back contact of relayBD, the No. 2 right front contact of operated relay CD, the No; 2 right back contact of relay AU, the No. 3 right back contact of relay BU, the No. 5 right front contact of operated relay CU, 'conductor |332, the No. 3 'left contacts of progress relay |401, to battery through the right winding of relay |402 'of the A code digit register. Relay |402 thereupon operates and locks over its left winding and left contacts to ground on conductor |303 and with the remaining relays |40|, |404, |405 and |400 of the A register unoperated, serves to register the rst code letter C.

A circuit is also established upon the operation of relay |305 over its lower front contact. the lower back contact of relay |306, over the outer right front contact of relay |32| to battery through the winding of relay |322, which operates after an interval sufficient to insure that the digit signals recorded through the operation of recording relays have been eiective to cause the registration thereof in a digit register of the sender; at its back contact .opens the locking circuits .of the operated recording relays, in the case assumed relays CD and CU, which thereupon release; opens the locking circuit of transfer relay |32| 'which releases and at its front contact establishes an obvious circuit for relay |325. Relay |325 operates, locks over its right contacts to o-normal ground on conductor |303 and at its left contacts prepares a 'circuit for operating the progress relay |4|6. When relay |32| releases relay |322 also releases.

When the subscriber depresses the key K4 to transmit impulses for the second oiTlce code letter H which has a numerical value of 4, the offnormal switch assembly '0 is operated momentarily to open the direct current loop at the substation and to connect the generator G to the substation line. During the interval that the switch is thus operated the reed Rc is released to 4transmit an impulse of the frequency c which,

upon being received in the receiving channel Fc of the sender results in the operation of channel relay |3|`| and. with transfer relays |32| Anow released, in the operationof recording relay CD overthe circuit previously traced. Relay CD upon operating locks under the control of relay |322 and prepa-res thecircuit of relay |32| as previously described. When the line loop is opened at the substation by the-oil'normal switch assembly, relay |202 releases and by removing j ground from conductor |2|'| permits relay |303 to operate in the manner previously described. With relays |305- and |305 now both operated and relay |325 operated, a circuit, is established from ground over the lower 4-front contact of relay |305, the lower front contactv of relay |305, thel A left contacts of relay |325, conductor |3|2, the

right front contact of progress relay |405 to bat,

tery through the winding of progress relay |4|0 which operates and locksthrough its winding and the winding of progress relay |4|1 over the left contacts of relay |4|8 and the back contact of progress relay |421 to ground on conductor |303. Relay |4|1 being shunted so long as ground remains connected to conductor |3|2, does not operate.

At the endof the iirst impulse for the second code digit, with the off-normal switch assembly 0 restored, the transmission of the frequency c ceases, channel relay |3|1 releases, and the directcurrent loop is reestablished at the substaytion resulting in the reoperation of relay |202 and the reconnection of ground to conductor 2| 1. As before described relay |306 is now held operated to this `ground and relayv |305 is shunted and releases. With relay |305 released and relay |306 operated, the circuit for transfer relay |32|, previously` prepared through the operation of recording relay CD, is completed and relay |32| operates and locks as previously described under the control of relay |322. Relay |305 upon releasing also removes ground from conductor |3|2 whereupon progress relay |4|1 operates in the locking circuitof relay MIB; connects the Windings of the relays of the B code digit register to conductors |33I, |332, |334, |335 and |330, extending to contacts of the recording relays and at its right back contacts opens the locking circuit of relays |405 and |401 which now release since their operating circuit was openedl upon the previous operation of relay |309.

Upon the up-stroke of the depressed key K4 the' off-normal switch assembly 9 is 'again operated momentarily to open the direct current loop at the substation and to connect the generator G tothe substation line. During the interval that the switch is thus operated the reed Rb is released to transmit the frequency b which upon being received in the receiving channel Fb of the sender results in the operation of channel relay |324 and, with transfer relay |32| now operated, in the operation of recording relay BU over a circuit extending from ground over the contacts of relay 324, the inner left front contacty of relay |32| to battery through the winding of relay BU. Relay BU upon operatingv locksover releases to terminate the second frequency impulse, relay |202 again operates thereby causing the reoperation of relay |305 over the circuit previously traced. With relay |305 operated and relay |306 unoperated, a circuit is established from ground over the lower front contact of relay |305, the lower back contact of relay |306, the right back contact of relay AD, the No. 2 back contact of relay BD, the No. 2 front contact of relay CD, the No. 2 back contact of relay AUgthe No. 3 front contact of relay BU, the No. 4 back contact of relay CU, conductor |334, the No. 4 front contacts of progress relay |4|1 to battery through the right winding of relay 4| 4 ofthe oilice code register B. Relay |4|l upon operating in this circuit locks over its left winding and left contacts to ground on conductor |303 and with the remaining relays of the B register unoperated serves to register the second oiflce code letter H.

The operation of relay |305 with relay |306 unoperated also establishes the previously traced circuit for relay |322 which operates after an interval to cause the release of the operated recording relays CB and BU and the release of the transfer relay |32|. When relay |32| releases, relay |322 also releases. y

When the subscriber depresses the key K3 to transmit impulses for the third code digit 3, the off-normal switch assembly 9 is operatedmomentarily to open the directcurrent loop at the substation and to connect the generator G to the substation line. During the interval that the switch is thus operated the reed Rb is released to transmit an impulse of the frequency b whichupon being received in the receiving channel Fb of the sender results in the operation of the channel relay |324 and, with transfer relay |32i not operated, in the operation of recording relay BD over a circuit extending from ground over the contacts of relay |324, the inner left back contact of relay |32| to battery through the winding of relay BD. Relay BD upon operating locks under the control of relay |322 and prepares the circuit of relay |32I as previously described. When the line loop is opened at the substation by the olf-normal switch assembly relay |202 releases and by removing ground from conductor |2|1 permits relay |305 to operate in the manner previously described. With relays |305 and |306 now both operated and relay |325 operated, a circuit is established from ground over the lower front contact of relay |305, the lower front contact of relay |306, the left contacts of relay |325, conductor |3|2, the right back contact of relay |406, the right front contact of relay |4|6, to battery through the winding of progress Vrelay |426. Relay |426 operates and locks through its winding and the winding of progress relay |421,

Vover the left contacts of relay |426 and to ground on conductor |303, over the back contact of the progress relay- (not shown) associated with the thousands digit register and corresponding to progress relay |421. Progress relay |421 being shunted does not operate so long as ground remains connected to conductor |3|2.'

At 'the end of .the first impulse `for the third code digit with the off-normal switch assembly 9 restored, the transmission of the frequency b ceases, channel relay |324 releases and the direct current loop is reestablished at the substation resulting in the reoperation of relay |202 and rel connection of groundy to conductor |2|'|. As before described, relay |305 is now held operated to this ground and relay|305 is shunted and releases. With relay |305 released and relay |306 operated a circuit for transfer relay |32|, previously prepared through the operation of recording relay BD, is completed and relay |32| operates and locks as previously described under the control of relay |322. Relay |305 upon releasing also removes ground from conductor |3|2 whereupon progress relay 5421 operates in the locking circuit of relay |423; connects the windings of the relays of the C code digit register to conductors |33l, |332, |334, |335 and |330 extending to contacts of the recording relays and at its right back contact opens the locking circuit of relays |4|6 and |4|1 which now release since their 0perating circuit was opened upon the removal of ground from conductor I3 I 2.

Upon the up-stroke of the depressed key K3 the off-normal switch assembly 9 is again operated momentarily to open the direct current loop at the substation and to connect the generator G to the substation line. During the interval that the switch is thus operated the reed Rb is released to transmit the frequency b which upon being received in the receiving channel Fb of the sender results in the operation of the channel relay |324 and, with transfer relay 32| operated, in the operation of recording relay BU. Relay BU upon operating locks over its left contacts under the control of relay 322.

When the olf-normal switch assembly 9 again releases to terminate the second frequency irnpulse, relay |202 again operates thereby causing i306, the right back contact of relay AD, the No.

3 right front contact of relay BD, the No, 3 right back contactof relay CD, the No, 3 right back Contact of relay AU, the No. 5 right front contact of relay BU, the No. 6 right back contact of relay CU, conductor |33l, the No, 2 left contacts of progress relay to battery through the right winding of relay |42| of the code digit register C, and a second circuit is established from ground applied over the right back contact of relay AD, the No. 4 right front contact of relay BD, the No. 4 rightback contact of relay CD, the No. 4 right back contact of relay AU, the No. 7 right front contact of relay BU, the No. 5 right back contact of relay CU, conductor |332, the No. 3 left contacts of progress relay |421 to battery through the right winding of relay |422 of the code digit register C. Relays |42| and |422 upon operating lock over their left windings and left contacts to ground on conductor` |303 and with the other relays of the C code digit register unoperated serve to register the third cnice code digit 3.

'I'he operation of relay |305 with relay |306 unoperated also establishes the previously traced circuit of relay |322 which operates after an interval to cause the release of the operated recording relays BD and BU and the release of transferrelay |32| followed by the release of relay |322.

` In a similar manner in response to the keying of the thousands numerical digit 1 two impulses Iof frequency a are sent resulting in the operation followed by an impulse of frequency a are sentv resulting in the operation of recording relays BD and AU.

With recording relays AD and AU operated to recordthe receipt' of signal impulses for the thousands digit 1, then when ground ls applied to the right armature of relay vAD, a circuit is established over the right front contact of relay AD, the No. 1 right back contact of relay BD, the No. 1 right back contact of relay CD, the No.

- l iight front contact of relay AU, the No. 2 right back contact of relay BU, the No. 6 right back contact of relay CU to conductor |33| and thence over the No, 2 left contacts of an operated progress relay, similar to relay |401 but associated with the thousands digit 'reglster, to battery through the winding of a relay of that register corresponding to relay |40| whereby such relay operates and locks and with the other relays of such register unoperated registers the thousands digit 1.

With the recording relays CD, AU and BU operated to record the receipt of signal impulses for the hundreds digit then when ground is applied to the right armature of relay AD, a. circuit is established over the right back contact of relay AD, the No. 2 right back contact of relay BD, the No. 2' right front contact of relay CD, the No. 2 right front contact of relay AU, the No. 2 right front contact of relay BU, the No. 3 right back contact of relay CU to conductor |330 and thence over the No. 1 left contacts of an operated progress relay, similar to relay |401 but associated with the hundreds digit register, to battery through the winding of a relay of that register corresponding to relay |400 whereupon such relay operates and locks to register the hundreds digit 0.

With recording relays CD and AU operated to record the receipt of signal impulses for the tens digit 6, then when ground is applied to the right armature of relay AD a first circuit is completed over the right back contact of relay AD, .the No. 2

right back contact of relay BD, the No. 2 rightfront contact of relay CD, the No. 2 right front contact of relay AU, No. 2 right back contact of relay BU, the No. 6 right back contact of relay CU, conductor |33| and thence over the No. 2 left contacts of an operated progress relay, similar to relay |401 but associated with the tens digit register, to battery through the winding of a relay of such register corresponding to relay |40| whereupon such relay operates and locks. A second circuit is also established from ground applied over the right back contact of relay AD, the No. 2 right back contact of relay BD, the No. 6 right front contact of relay CD, the No. 6 right front contact of relay AU, the No. .4 right back contact of relay BU, the No. 1 right back contact of relay CU, conductor |335 and thence over the No. 5 left contacts of an operated progress relay, similar to relay |401 but associated with the tens digit register, to battery through the winding of a relay of that register corresponding to relay |405 which thereupon operates and locks. With these two register relays operated and the other relays of the tens digit register unoperated, the tens digit 6 is registered.

18 With recording relays BD and AU operated to record the receipt of signal impulses for the units digit 7, then when ground is applied to the right contact of relay AU, the No. 6 right backconl armature of relay AD, a first circuit is completed over the right back contact of relay AD, the No. 4 right front contact of relay BD, the No, 4 right back contact of relayiCD, the No. 4 right front tact of relay BU, the No, 5 right back contact of relay CU, over conductor |332 and thence over the No. 3 contacts of the operated progress relay |461, to battery through the right winding of relay |462 of the units digit register U. A second circuit is also completed over Ithe right back contact of relay AD, the No. 3 right front contact of relay BD, the No. 3 right back contact of relay CD, the No. 3 right front contact of relay AU, the No. 4 right back contact of relay BU, the No. l right back contact of relay CU, conductor i335 and thence over the No. 5 contacts of relay i461 to battery through the right winding of relay |465 of the units digit register U. Relays |452 and |465 upon operating lock over their left windings and left contacts to ground on con- .ductor |303 and with the other relays of this reg- .registration of letters or digits having the'digit values 1, 2, 3, 4, ;6, 7 and 0 have been described. If the digit 5 is keyed by the operation of key K5 thenan impulse of frequency a would be sent followed by an impulse of frequency b resulting in the operation of recording relays AD and BU. With these relays operated then when ground is applied 'to the right armature of relay AD, a circuit is completed over the right front contact of relay AD, the N0. 1 right back'contact of relay BD, the No. 1 right back contact of.relay CD, the No. 1 right back contact of relay AU, the No. 1 rightfront contact of relay BU, the No. 1 right back contact of relay CU to conductor I 335 to as relay |405 of the first code digit register A.

If the digit 8 is keyed by the operation of keyv K8, then an impulse of frequency a is sent followed by an impulse of frequency c resulting in the operation of recording relays AD and CU. With these relays operated then when ground vis applied to the right armature of relay ADa rst circuit is completed over the right front contact of relay AD, the No. 1 right back contact of relay BD, the No. 5 right back contact of relay CD, the No. 5 right back contact of `relay AU, the No. 8 right back contact of relay BU and the N o. 6 right front contact of relay CU to conductor 133|; a second circuit is completed over the right front contact of relay AD, the No. l right back contact of relay BD, the No. 1 right back contact of relay CD, the No. l right back contact of relay AU, the No. 1 right back contact of relay BU and the No. `2 right front contact of relay CU to conductor |332 and a, third circuit is established over the right back contact of relay AD, the No. 1 right back contact of relay BD, the No. `1 right back contact of relay CD, the No. 1 right back contact of relay AU, the No. 1 right back contact of relay BU and the No. 1 right iront contact of relay CU asoaevs i i@ to conductor |335. With ground applied to conductors |33|, |332 and |335 relays of. a digit register, such as relays |40i, |402, |405 of the iirst code digit register A are operated to register the digit 1 If the digit 9 is keyed by the operation of key K9, then an impulse of frequency b is sent followed by an impulse-of frequency c resulting in the operation of recording relays BD and CU. With these relays operated, then when ground is supplied to the right armature of relay AD, a rst circuit is completed over the right back contact of relay AD, the No. 3 right front contact of relay BD, the No. 3 right back contact ofV relay CD, the No. 3 right back contact of relay AU, the No.5 right back contact of relay BU and the No. 4 right front contact of relay CU to conductor |334 and a second circuit is established from' ground over the right back contact of relay AD, the No. 4 right front contact of relay BD, the No. 4 right back contact of relay CD, the No. 4 right back contact of relay AU, the No. 7 right back contact of relay BU and the No. '7 right front contact of relay CU to conductor |335. With ground applied to conductors |334 and |335, relays of a digit register such as relays |404 and |405 of the rst code digit register A are operated to register the digit 9.

What is claimed is:

1. In a telephone system in which the selection of wanted lines is eiected by transmitting over a line extending from a calling station impulse combinations made up of a, plurality of frequencies within the voice-frequency range, an impulse generator at the calling station comprising a plurality of diierently tuned reeds vibratable in an electromagnetic field, a plurality of keys each having a down-stroke and an up-stroke movement and means controlled by said keys 'for selectively operating said reeds for causing the trans-l mission of one impulse of a combination during the down-stroke of a key and for selectively operating said reeds for causing the transmission of theremaining impulse of a. combination during the up-strcke of the operated key.

2. In a telephone system in which the selection of wanted lines is effected by transmitting .over a line extending from a calling station impulse coml binations made up of a plurality of frequencies within the voice frequency range, an impulse generator at the calling station comprising three differently tuned reeds vibratable in an electromagnetic iield, a plurality of keys each having a down-stroke and 'an up-stroke movement and means controlled by said keys for selectively operating one of said reeds for causing the transmission of one impulse of a combination during the down-stroke of a key and for selectively operating one or two of said reeds for causing the transmission of the remaining impulse of a combination during the up-stroke of the operated key.

3. In a telephone system in which the selection of wanted lines is eiected by transmitting over a line extending from said calling station impulse combinations made up of a plurality of frequencies within the voice frequency range, an impulse generator at the calling station comprising a` plurality of differently tuned reeds vibratable in an electromagnetic iield, a.plurality of keys each having a down-stroke and an up-stroke movement, a timing switch momentarily operable once during tliedown-stroke of an operated key and again duringy the 11p-stroke of an operated key. and means controlled by said keys for selectively operating said reeds for causing the transmission of one impulse oi' a combination, timed by said switch, during the down-stroke of a key impulse generatorV at the calling station comprising a plurality 'of differently tuned pretensioned reeds vibratable in an electromagnetic field, a releasing member associated with each of said reeds, a plurality of keys each having a down-stroke and an up-stroke movement, a pair of bars associated with each of said reedreleasing members, means `controlled by the operation of the rst bar of any pair for operating the associated reed-releasing member. means controlled by the release of the second bar of any pair when operated for operating the associated reed-releasing Imember and means controlled by said keys for selectively operating and then releasing said bars to cause the selective operation of said reed-releasing members, whereby one impulse of a combination is transmitted during the down-stroke of a key and the Aremaining impulse of a combination is transmitted during the up-stroke of the operated key.

5. In a telephone system in which the selection of wanted lines is effected by transmitting over a line extending from a `calling station impulse combinations of frequencies within the voice frequency range, an impulse generator at the calling station comprising a plurality of difierently tuned pretensioned reeds vibratable in an electromagnetic field, a release member associated with each of said reeds, a plurality of keys each having a down-stroke and an upstroke movement, a pair of depressible bars associated with each of said 'reed-releasing members, means controlled by the depression of the first bar of any pair for operating the associated reed-releasing member, means controlled by the releasing movement of the second bar-of any pair, if depressed, for operating the associated reed-releasing member, and means controlled by said lkeys for selectively depressing and then releasing said bars to cause the selective operation of said reed-releasing members, whereby one impulse of a combination is transmitted during the down-stroke of a key and the remaining' impulse of a combination is transmitted during the up-stroke of the operated key.

6. In a telephone system in which the selection of wanted lines is eiected by transmitting over a line extending 'from a calling station impulse combinations of frequencies within the voice frequency range, an impulse generator at the calling station comprising a plurality of difierently tuned pretensioned reeds vibratable in an electromagnetic `field, a releasing member associted with each of said reeds, a rotatable cam for operating each releasing member.' a plurality of keys each having a down-stroke and an up-stroke movement, a pair of depressible bars associated with each of said cams, a ratchet assembly controlled by the depression of the rst bar of any pair for rotating said cam to operate the associated reed-releasing member, a ratchet assembly controlled by the releasing movement oi the said cam to operate the associated reed-releasing mem-berand means associated with said keys for selectively depressing and then releasing said bars to cause the selective operation of said reedreleaslng members, wherebyone impulse' of a combination is transmitted during the downstroke of a key and the remaining impulse of the combination is transmitted during the upstroke of the operated key.

7. In a telephone system in which the selection of wanted lines is eiiected by transmitting over a line extending from a calling station impulse combinations of frequencies within the voice frequency range, an impulse generator at the calling station comprising a plurality oi' diierently tuned pretensioned reeds vibratable in an electromagnetic held, a releasing member associated with each of said reeds, a rotatable cam for operating each releasing member, a pair of ratchet assemblies associated with each of said cams. a pair of depressible bars associated with each pair o! ratchet assemblies. one of said bars being eiective upon its depression through one of said associated ratchet assemblies to rotate the associated cam to operate the associated reed-releasing member and the other of said bars being eiIective upon its releasing movement. if depressed'. through the other of the associated ratchet assemblies to rotate the associated cam to operate the associated reedreleasing member. a plurality of keys each having a down-stroke and an up-stroke movement and means associated with said keys for selectively depressing and then releasing said bars to selectively operate said reed-releasing members, whereby one impulse of a combination is transmitted during the down-stroke of a key and the remaining impulse of the combination is transmitted during the up-stroke of the operated key.

l HENRY M. BASCOM.

FRANCIS A. HUBBARD. 

